1930: The first documented reference to an electronic cigarette is a patent granted to Joseph Robinson in 1930 (filed in 1927). It was never commercialized and it is not entirely clear that even a prototype of this primitive device was manufactured.
1960s: Herbert A. Gilbert is generally credited with the creation of the first device that closely resembled the modern e-cigarette. He reports receiving a patent in 1965 (filed in 1963) and created prototypes (possibly never including nicotine), but failed to commercialize it. He attributes this failure the companies who might have commercialized it preferring to wait for the patent to expire rather than license it, though it is not clear whether it had commercial potential at the time.
1979-80s: Starting in 1979, Phil Ray, one of the pioneers of computers, worked with his personal physician Norman Jacobson to create the first commercialized variation on the e-cigarette (which was not actually electronic; it relied on evaporation of the nicotine). They performed the first known formal research in the field on nicotine delivery. The commercialization of the product reached major retailers. But the device was never a promising technology for nicotine delivery; Jacobson attributes its failure to it being inherently faulty. While the device proved to be a dead-end, the inventors did contribute the verb “vape” to the language.
1990s: Numerous patents for nicotine inhaler devices were filed throughout the 20th century and early 2000s by both tobacco companies and individual inventors, with a flurry of activity in the 1990s. Many relied on evaporation or physical propulsion, but a few were fairly similar to modern e-cigarettes. One chemical-reaction based system that was invented in the 1990s is still in the pipeline. Reynolds brought to market the Eclipse “heat-not-burn” device, whose functioning falls somewhere in between that of a pure nicotine inhaler and a combusted cigarette. (See also Philip Morris’s Accord.) Products closely resembling modern e-cigarettes moved toward commercialization in the 1990s (example). A major U.S. tobacco company requested permission from FDA (which did not then regulate tobacco products, but did regulate drug delivery devices) to bring a version of an e-cigarette to market c.1998. FDA denied the request on the basis of it being an unapproved drug delivery device. This may explain the disappearance of the attempts to bring an e-cigarette to market, though the history of what happened is rather murky, and the U.S. ruling does not fully explain the disappearance of the technology elsewhere.